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C 0 R - - - I PREVIOUS INVESTIGATIONS AND REMEDIAL ACTION Page 1 I A & A Tank tested the four tanks on the site on July 26, 1988 They reported that they were unable to test the 12,000-gallon tank and that the two 6,000-gallon tanks, containing diesel and regular gasoline, failed the tightness test A & A Tank retested the tanks on August 10, 1988, and reported that the 10,000-gallon, the 12,000-gallon, and the 6,000-gallon diesel tank tested tight Information on a retest of the 6,000-gallon tank containing regular gasoline could not be found LCI tested the four underground storage tanks (UST)s on September 14, 1989, and reported that the test on the 6,000-gallon regular tank was terminated due to high product loss A release report was filed with San Joaquin County on October 6, 1989 The tank was repaired and passed a tightness test conducted on September 27, 1989 The 6,000-gallon regular tank failed a tightness test conducted on September 26 and November 6, 1990 A release report was fled with the county on October 5, 1990 The tank was repaired and passed a subsequent tightness test RESNA conducted a preliminary assessment of the site in December 1992 Four exploratory borings were drilled to depths of approximately 46 5 feet bgs Borings B-1 and B-2 were drilled in the vicinity of the UST complex Borings B-3 and B4 were drilled southwest of the dispenser islands and associated piping The soil types encountered at the site generally consisted of silt and sand to a depth of 46 5 feet bgs Groundwater was not encountered • Soil samples were collected from each boring at depths of 10 and 45 feet bgs (except for boring B-4, where the samples were collected at depths of 30 and 45 feet bgs) and submitted for laboratory analysis for GRO and BTEX BTEX (up to 0 088 ppm benzene, 0 052 ppm toluene, 0 0067 ppm ethylbenzene, and 0 041 ppm xylenes) was detected in four of the eight samples The highest concentrations were detected in the sample collected at the 10 foot bgs level in boring B-2 In addition, MTBE was detected in samples from B-1 and B-2 at 10 feet bgs (0 096 and 0 37 ppm, respectively) A sensitive receptors survey was contained in RESNA's preliminary site assessment report The report, dated February 2, 1993, stated that a public water supply well was located approximately 2,000 feet from the site, and a private water supply well was located approximately 300 feet from the site The aquifer was classified Class II Current and Potential Drinking Water Source The San Joaquin County Public Health Services reviewed the RESNA report and requested that BP drill another soil boring in the vicinity of boring B-4 (southwest of the northern pump island) This additional soil boring (B-5) was drilled slightly east of boring B-4 to a depth of 60 5 feet Soil encountered during drilling consisted predominantly of sand and clayey silt with trace silt and fine gravel Groundwater was not encountered Soil samples from 36 5, 46 5, 51 5, and 60 5 feet bgs and a composite from the stockpiled drill cuttings were analyzed for GRO and BTEX The sample from the drill cuttings was also analyzed for lead, reactivity, corrosives, and ignitability BTEX was detected in the soil sample collected at 46 5 feet bgs (0 15 ppm benzene, 0 13 ppm toluene, 0 014 ppm ethylbenzene, and 0 04 ppm xylenes), and benzene at 0 0093 ppm was detected in the soil sample collected at . 51 5 feet bgs TPH-G at a level of 5 3 ppm was detected in the sample from the drill cuttings